The primary purpose of this research project is to determine the occurrence of elevated serum antibodies to the periodontal pathogens Actinobacillus actinomycetemcomitans (A.a.) and Porphyromonas gingivalis (P.g.) in a normal population. The study population is comprised of persons aged 13+ examined in Phase I of the Third National Health and Nutrition Examination Survey (NHANES III). Serum from the NHANES III subjects, which has already been collected, frozen, and stored, will be assayed by ELISA procedures. The ELISA offers the benefit of quantification of antibody titers; values of 100 EU or greater for A.a. and 20 EU or greater for P. gingivalis will be employed as threshold values for designating elevated levels. The prevalence of elevated antibody titers to these organisms will be described for the entire sample and stratified by age, gender, race, and geographic region. Systemic antibody titers also will be correlated with the clinical periodontal status of study participants.